This is a 30-40mm fan adapter specifically designed to work inside the Unifi XG 16 switch. The original fans are noisy, and the 1U case can hold a 40mm fan. It's specific to the case because there is interference with the upper case lid when closing the lid that needs to be avoided.
This part is designed to replace the 30mmx30mmx15mm fans with Noctua 40mmx40mmx20mm. Do not use a deeper 40mm fan than 20mm, as it will then interfere with the mainboard of the switch.
Inspired by design here https://www.thingiverse.com/thing:4143421 and the blog post at https://blog.pcfe.net/hugo/posts/2020-03-06-us-16-xg0-fan-mod/, I decided to do my own (not a remix, but a new from scratch design). I figured I could get a slightly more organic shape and better airflow.